Manual Therapy 19 (2014) 165e168
Contents lists available at ScienceDirect
Manual Therapy journal homepage: www.elsevier.com/math
Technical and measurement report
Sonographic measurement of the normal suprascapular nerve and omohyoid muscle Patrick J. Battaglia a, *, Daniel W. Haun a, Kathy Dooley b, Norman W. Kettner a a b
Department of Radiology, Logan University, 1851 Schoettler Road, Chesterfield, MO 63006, United States Einstein College of Medicine of Yeshiva University, United States
a r t i c l e i n f o
a b s t r a c t
Article history: Received 16 July 2013 Received in revised form 1 December 2013 Accepted 17 December 2013
The aim of this study was to obtain normative ultrasonography (US) data on the suprascapular nerve (SSN) and omohyoid muscle (OM) in the lateral cervical region. The SSN and OM are known to be related throughout the nerve’s course, yet little imaging data exists on these structures at areas more proximal than the suprascapular foramen. US data from a convenience sample of 33 asymptomatic subjects between 21 and 42 years of age were collected. Cross sectional area (CSA) of the SSN, distances from the OM to the SSN, and long-axis diameter of the OM at three reference points were obtained. The mean CSA of the SSN at both its origin and over the first rib was 1.9 mm2 and at the distal clavicle was 2.0 mm2. The mean distance of the OM to the SSN at these locations was 7.6 mm, 4.2 mm and 2.8 mm respectively. The mean long axis diameter of the OM was 2.4 mm at the SSN origin, 3.4 mm at the first rib, and 4.1 mm at the distal clavicle. We present US data from asymptomatic subjects on the SSN and OM. Our results show that the SSN nerve CSA is consistent throughout the nerves proximal course. Furthermore, the OM and SSN tend to approximate as they course distally. Future studies with larger samples will better characterize the normal sonoanatomy of these structures between genders and across different ages. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: Suprascapular nerve Omohyoid muscle Ultrasonography
1. Background The suprascapular nerve (SSN) courses deep and parallel to the omohyoid muscle (OM) from its origin off the upper trunk of the brachial plexus in the lateral cervical region to its passage through the suprascapular foramen (Standring, 2008). The OM muscle begins as a superior belly originating from the hyoid bone, narrowing to a central tendon behind the sternocleidomastoid muscle, and continues as an inferior belly to attach to the medial aspect of the suprascapular foramen (Standring, 2008). The inferior belly of the OM is also known to variably attach to the superior transverse scapular ligament (Standring, 2008). During the act of deglutition, the OM functions to depress an elevated hyoid bone (Standring, 2008). Despite this intimate relationship, no research has described the potential for, or actual entrapment of, the SSN by the OM. Furthermore, there is no research describing the effects of seatbelt trauma on either the OM or SSN in whiplash injury, even though a considerable number of patients diagnosed with whiplash associated disorder present with combined neck and shoulder pain and altered scapular alignment (Hincapie et al., 2010; Helgadottir * Corresponding author. Tel.: þ1 (636) 230 1832; fax: þ1 (636) 207 2429. E-mail addresses: [email protected], [email protected] (P. J. Battaglia). 1356-689X/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.math.2013.12.005
et al., 2011). The aim of this current study was to quantify the in vivo anatomy of these structures in healthy subjects, so that future work may be done on symptomatic cohorts. The SSN is a mixed motor and sensory nerve receiving contributions from the C5 and C6 nerve roots, and occasionally the C4 nerve root (Freehill et al., 2012). The nerve supplies approximately 70% of the sensory innervation to the shoulder joint and provides motor innervation to both the spinatus muscles (Freehill et al., 2012). The SSN also has a variable cutaneous distribution (Ajmani, 1994). Suprascapular neuropathy has been shown to be absent in patients with cervical radiculopathy who present with shoulder pain (Date and Gray, 1996). However, cysts within the glenoid cavity can mimic cervical radiculopathy (Uppal et al., 1995), and ruling out cervical spine pain referral is important in the physical exam of shoulder pain (Date and Gray, 1996). Currently, no research has reported the cross-sectional area of the SSN in the lateral cervical region of the neck in patients with suprascapular neuropathy or cervical radiculopathy. Recent work on the use of ultrasonography (US) to assess the SSN at a level more proximal than the scapula was done by Siegenthaler and colleagues (Siegenthaler et al., 2012). In their study they performed US on 60 healthy volunteers and determined that visualization of the SSN with US is better in the lateral cervical region than at the level of the scapula and that the OM provided a
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reliable anatomical landmark as it is clearly seen deep to the sternocleidomastoid muscle (Siegenthaler et al., 2012). Unfortunately, because their study was done to validate a novel nerve block approach, the only data provided was the nerve’s depth under the skin and distance to the brachial plexus (for nerve block safety). Also, the authors set a 1 min time limit per subject for their US scan to simulate the time constraints of their practice. This led to nonvisualization of the nerve in certain cases. Therefore, the purpose of this study was to obtain normative US data on both the SSN and OM in healthy subjects beginning at the SSN origin to as far distal as our scanning technique and participant anatomy would allow. Quantification of these structures with US may aid in future determination of suprascapular neuropathy or suspected OM damage and SSN entrapment/irritation.
standardized points: Point 1 (pt. 1), emergence of the nerve off of the superior trunk; Point 2 (pt. 2) lateral aspect of the first rib; Point 3 (pt. 3) most distal aspect of the clavicle which could be imaged. The OM was assessed in the long axis and diameter measurements were obtained at these same three standardized points. Vascular variants detected during the examination were also noted.
2. Method
A total of 33 healthy volunteers (11 female; age range 21e42; mean age 26.2 years) participated in the study. Descriptive results are presented in the Table 1. Of the 33 subjects, the dominant hand was scanned in five cases as these subjects reported mild neck and/ or shoulder discomfort on the non-dominant side. None of the subjects reported sustaining trauma to the neck or shoulder within the past three months. There were five right-sided and 28 left-sided scans. The SSN was easily visualized in all 33 scans (Figs. 1e4), and its cross-sectional area remained consistent through its visualized course in 29 of these scans. In the four nerves that changed size during their course, two increased from a value of 1 mm2 at their origin to 2 mm2, one decreased from a size of 3 mm2 at its origin to 2 mm2, and one measured 3 mm2 at its origin, 2 mm2 at the lateral aspect of the first rib, and 3 mm2 at the distal clavicle. When assessing for the distance from the OM to the SSN at the nerve’s origin, most subjects displayed consistent anatomy with the inferior belly being the portion of the muscle present. In three of our subjects the central tendon, not the inferior belly, was present adjacent to the origin of the SSN, with distances between these two structures of 7.5 mm, 8.6 mm and 11.8 mm respectively. One subject had the superior belly of the OM present at the SSN origin with a distance between the two of 6.4 mm and a long axis diameter of 2.6 mm. Four of our research participants had a blood vessel coursing between the SSN and OM.
2.1. Participants Participants were recruited internally through university advertisements and were selected if they were between the ages of 18e65 years, had no history of fracture, dislocation or surgery to the cervical spine or shoulder, reported no trauma to the cervical spine or shoulder within the past three months, and currently were not experiencing neck and/or shoulder pain. Presence of the following conditions also excluded participation from the study: diabetes mellitus, rheumatoid arthritis, neurofibromatosis, and myelopathy, radiculopathy and peripheral nerve entrapment. Patients were screened for the exclusion criteria by a senior intern with one year of experience in diagnosing and treating musculoskeletal conditions. Approval was obtained from the university institutional review board and each participant gave signed consent prior to participation. 2.2. Procedure US scans of all subjects were performed using a GE LOGIQ e US system with an 8e12 MHz linear transducer (GE Healthcare, Milwaukee, WI) operating at 10 MHz. All US scans were performed by the same board-certified chiropractic radiologist with six years of experience in musculoskeletal ultrasound. For the purpose of this study, no formal reliability testing was performed. Participants were gowned and seated in the same position for the duration of the scan, which was approximately 15 min. Each participant had their non-dominant lateral cervical region and supraclavicular fossa scanned. In instances when the participant reported either past trauma to the non-dominant side or a history of neck and/or shoulder pain in the last three months to the non-dominant side, the dominant side was used for scanning. When studying nerve cross-sectional area, it is acceptable to use the healthy contralateral side as an internal control (Tagliafico and Martinoli, 2013). The superior belly of the OM was identified immediately deep to the sternocleidomastoid muscle as it coursed from medial to lateral from its superior attachment to the hyoid bone. Identification was made with the transducer in the axial plane using a series of shortaxis linear slides in a superior to inferior direction. The superior belly of the OM was followed to its central tendon and inferior belly of OM and then as far inferiorly and laterally as possible until shadowing from the clavicle prevented further visualization. The C5 and C6 nerve roots were identified in the axial plane using previously established approaches (Siegenthaler et al., 2012) and were followed until they became the superior trunk of the brachial plexus. The SSN was identified as it emerged from the upper trunk of the brachial plexus at Erb’s point. Cross-sectional areas of the SSN as well as distances to the OM were measured at three
2.3. Data analysis Descriptive statistics were applied using Microsoft ExcelÔ 2010 (Microsoft, Inc., Bothell, WA). Mean, standard deviation (SD), SD range 2 and range were calculated. 3. Results
4. Discussion The SSN and OM follow similar courses through the lateral cervical region as they approach the scapula, and our results indicate that they are on average less than 1 cm apart during their Table 1 Descriptive statistics. Data point (n ¼ 33)
Mean
SD
SD range (2)
Cross sectional area (mm2) SSN e pt. 1 Cross sectional area (mm2) SSN e pt. 2 Cross sectional area (mm2) SSN e pt. 3 Linear distance (mm) OM to SSN e pt. 1 Linear distance (mm) OM to SSN e pt. 2 Linear distance (mm) OM to SSN e pt. 3 Long axis diameter (mm) of OM e pt. 1 Long axis diameter (mm) of OM e pt. 2 Long axis diameter (mm) of OM e pt. 3
1.9
0.4
(1.6)e2.4
2(1e3)
1.9
0.2
(1.8)e2.2
1(1e2)
2.0
0.3
(1.7)e2.3
2(1e3)
7.6
4.6
2.6e6.6
18.2(0e18.2)
4.2
4.0
2.0e6.0
12.4(0e12.4)
2.8
3.3
1.3e5.3
11.5(0e11.5)
2.4
1.0
(1.0)e3.0
4.1(0e4.1)
3.4
0.9
(1.1)e2.9
3.7(1.8e5.5)
4.1
0.9
(1.1)e2.9
3.6(2.4e6)
Range (minemax)
P.J. Battaglia et al. / Manual Therapy 19 (2014) 165e168
167
Fig. 1. Short axis US image (left) and corresponding line diagram (right) of the SSN (arrowhead) and OM where the SSN emerges from the upper trunk of the brachial plexus (double arrowhead). The anterior scalene (AS) and middle scalene (MS) muscles are labeled to provide a reference for medial and lateral, respectively.
Fig. 2. Short axis US image (left) and corresponding line diagram (right) of the SSN and OM at the lateral aspect of the first rib. The trapezius muscle (asterisk) is also labeled.
Fig. 3. Short axis US image (left) and corresponding line diagram (right) of the SSN and OM at the distal clavicle. The trapezius muscle (asterisk) is also labeled.
Fig. 4. Long axis US image (left) and corresponding line diagram (right) demonstrating where diameter measurements were obtained on the OM (double vertical lines). The SSN is seen in long axis as a tubular structure (asterisk) immediately deep to the OM.
whole course from SSN origin until the distal clavicle, approximating during their path. Both the nerves cross-sectional area and the muscles diameter stay relatively constant within each individual subject, and narrow ranges exist for SSN cross-sectional area. Recent ultrasound work on the sciatic nerve in patients with sciatica and low back pain has demonstrated a significantly larger nerve on the affected side (Kara et al., 2012). Similar findings are
present in the median nerve in patients with carpal tunnel syndrome (French et al., 2012) and the greater occipital nerve in patients with unilateral occipital neuralgia (Cho et al., 2012). Although increases in nerve cross-sectional area appear to be attributable to local entrapment in both the median and greater occipital nerves, nerve root irritation from lumbar disc herniation may be an implicating factor in the increase in sciatic nerve cross-sectional
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areas in symptomatic persons (Kara et al., 2012). Presently, there have been no investigations into the relationship between SSN cross-sectional area in the lateral cervical region in subjects with suprascapular neuropathy or cervical radiculopathy. Our results provide preliminary normative data on the nerve cross-sectional area in this region. Clinically, the OM is implicated in what is known as the omohyoid sling syndrome, a condition that presents with a painless mass in the lower part of the neck apparent when swallowing but absent otherwise (Wong and Li, 2000). Patients may also present with difficulty swallowing or similar morbidities prompting surgical excision; however, operations are usually performed for cosmetic indications (Wong and Li, 2000). There is only one report in the orthopedic literature which describes the potential for brachial plexus irritation secondary to an increase in omohyoid size (Fiske, 1952). However, since Fiske’s report is of one subject, it is of little clinical utility. Furthermore, the findings presented in this report have not been reproduced since its publication over sixty years ago. Nevertheless, those who suffer from whiplash associated disorders rarely present with isolated neck pain and frequently the shoulder is also a significant source of discomfort (Hincapie et al., 2010). Additionally, scapular and cervical spine alignments change in those with both an insidious onset of neck pain and whiplash-associated disorder (Helgadottir et al., 2011). Since it attaches to both the scapula and hyoid bone, it is plausible that altered shoulder girdle and cervical spine alignment would also alter the contraction pattern or position of the OM. Moreover, considering the placement of the seatbelt constraint across the neck, the potential does exists for acute traumatic injury of the OM and brachial plexus in a whiplash injury. In our study, we could readily locate and follow both the OM and SSN from the nerve’s origin in the lateral cervical region to the distal clavicle. It would be feasible to assess for alterations in the size of the OM or identify an associated hematoma from acute trauma as well as assess the SSN cross-sectional area for nerve entrapment or irritation. Four of our subjects had a blood vessel coursing between the SSN and the inferior belly of the OM consistent with the superficial (transverse) cervical artery (Muhly and Orebaugh, 2011). In addition to variations in the vasculature of the lateral cervical region, variations of the OM could also pose challenges to accurate sonographic assessment. While we did not appreciate any variations in the OM, there are several reported variations of the omohyoid muscle (Rai et al., 2008). Also, the cleidoatlanticus muscle, which is variably present and courses from the clavicle vertically through the lateral cervical region to attach to the transverse process of the atlas, has also been reported to alter the ultrasound image of this area (Feigl and Pixner, 2011). This study has several limitations. Although an experienced examiner performed all of the scans and measurements, intra- and inter-examiner reliability was not established in this study. However, US has been shown to have good to excellent intra-patient, intra-examiner, and inter-examiner reliability in quantifying peripheral nerves of the upper extremity (Tagliafico and Martinoli, 2013). Furthermore, US is also valid, in addition to reliable, when measuring peripheral nerves and skeletal muscles (Cartwright et al., 2013). Considering the superficial nature of the SSN and OM, it is anticipated reliability in measuring these structures with US would be comparable. Also, although 33 participants may be an adequate sample size, this was a convenience sample and no power analysis was performed. There was also a marked gender discrepancy (11 female to 22 male) and differences in nerve size amongst sexes cannot be accurately assessed. Furthermore, as this was a young age cohort, it is unclear what the normative measurements would be in an older sample. Future studies with a larger sample, broader age range and matched symptomatic subjects and controls
will better characterize the sonoanatomy of these structures. The use of electronic calipers permits measuring cross-sectional areas to the nearest mm, so it is possible that sub-millimetric differences in nerve size were present that could not be observed, however their clinical significance is not known. Lastly, because patient clavicle size, morphology, and shoulder position is highly variable and produces an inconsistent amount of shadowing, using the distal clavicle as a reference point is arbitrary. Improvements in the scanning technique in which an assistant depresses the clavicle and scapula while imaging the more distal aspects of the SSN and OM may provide more optimal images. 5. Conclusion We have reported normative US data on the SSN and OM in young, healthy subjects. Future studies with larger samples will better characterize the normal sonoanatomy of these structures between genders and across different ages. Knowledge of these values may be of use in assessing cases of combined neck and shoulder pain, especially if there has been seatbelt trauma. Acknowledgment The authors would like to thank Frank Scali, DC, for his preparation of the line artwork. References Ajmani ML. The cutaneous branch of the human suprascapular nerve. J Anat 1994;185:439e42. Cartwright MS, Demar S, Griffin LP, Balakrishnan N, Harris JM, Walker FO. Validity and reliability of nerve and muscle ultrasound. Muscle Nerve 2013;47(4):515e21. Cho JC, Haun DW, Kettner NW. Sonographic evaluation of the greater occipital nerve in unilateral occipital neuralgia. J Ultrasound Med 2012;31(1):37e42. Date ES, Gray LA. Electrodiagnostic evidence for cervical radiculopathy and suprascapular neuropathy in shoulder pain. Electromyogr Clin Neurophysiol 1996;36:333e9. Feigl GC, Pixner T. The cleidoatlanticus muscle: a potential pitfall for the practice of ultrasound guided interscalene brachial plexus blocks. Surg Radiol Anat 2011;33:823e5. Fiske LG. Brachial plexus irritation due to hypertrophied omohyoid muscle. J Am Med Assoc 1952;149(8):758e9. Freehill M, Shi LL, Tompson JD, Warner JJP. Suprascapular neuropathy: diagnosis and management. Phys Sportsmed 2012;40(1):72e83. French C, Cartwright MS, Hobson-Webb LD, Boon AJ, Alter KE, Hunt CH, et al. Evidence-based guideline: neuromuscular ultrasound for the diagnosis of carpal tunnel syndrome. Muscle Nerve 2012;46(2):287e93. Helgadottir H, Kristjansson E, Mottram S, Karduna A, Jonsson H. Altered alignment of the shoulder girdle and cervical spine in patients with insidious onset neck pain and whiplash-associated disorder. J Appl Biomech 2011;27(3):181e91. Hincapie CA, Cassidy D, Cote P, Carroll LJ, Guzman J. Whiplash injury is more than neck pain: a population-based study of pain localization after traffic injury. J Occup Environ Med 2010;52(4):434e40. Kara M, Levent O, Tiftik T, Kaymak B, Ozel S, Akkus S, et al. Sonographic evaluation of sciatic nerves in patients with unilateral sciatica. Arch Phys Med Rehabil 2012;93(9):1598e602. Muhly WT, Orebaugh SL. Sonoanatomy of the vasculature of the supraclavicular and interscalene regions relevant for brachial plexus block. Acta Anaesthesiol Scan 2011;55:1247e53. Rai R, Ranade A, Nayak S, Vadgaonkar R, Mangala P, Krishnamurthy A. A study of anatomical variability of the omohyoid muscle and its clinical relevance. Clinics (Sao Paulo) 2008;64:521e4. Siegenthaler A, Moriggl B, Mlekusch S, Schliessbach J, Haug M, Curatolo M, et al. Ultrasound-guided suprascapular nerve block, description of a novel supraclavicular approach. Reg Anesth Pain Med 2012;37(3):325e8. Standring S. Gray’s anatomy: the anatomical basis of clinical practice. 40th ed. Spain: Churchill Livingstone Elsevier; 2008. pp. 442e820. Tagliafico A, Martinoli C. Reliability of side-to-side sonographic cross-sectional area measurements of upper extremity nerves in healthy volunteers. J Ultrasound Med 2013;32(3):457e62. Uppal G, Uppal J, Dwyer A. Glenoid cysts mimicking cervical radiculopathy. Spine 1995;20:2257e60. Wong DSY, Li JHC. The omohyoid sling syndrome. Am J Otolaryngol 2000;21(5): 318e22.
Contents lists available at ScienceDirect
Manual Therapy journal homepage: www.elsevier.com/math
Technical and measurement report
Sonographic measurement of the normal suprascapular nerve and omohyoid muscle Patrick J. Battaglia a, *, Daniel W. Haun a, Kathy Dooley b, Norman W. Kettner a a b
Department of Radiology, Logan University, 1851 Schoettler Road, Chesterfield, MO 63006, United States Einstein College of Medicine of Yeshiva University, United States
a r t i c l e i n f o
a b s t r a c t
Article history: Received 16 July 2013 Received in revised form 1 December 2013 Accepted 17 December 2013
The aim of this study was to obtain normative ultrasonography (US) data on the suprascapular nerve (SSN) and omohyoid muscle (OM) in the lateral cervical region. The SSN and OM are known to be related throughout the nerve’s course, yet little imaging data exists on these structures at areas more proximal than the suprascapular foramen. US data from a convenience sample of 33 asymptomatic subjects between 21 and 42 years of age were collected. Cross sectional area (CSA) of the SSN, distances from the OM to the SSN, and long-axis diameter of the OM at three reference points were obtained. The mean CSA of the SSN at both its origin and over the first rib was 1.9 mm2 and at the distal clavicle was 2.0 mm2. The mean distance of the OM to the SSN at these locations was 7.6 mm, 4.2 mm and 2.8 mm respectively. The mean long axis diameter of the OM was 2.4 mm at the SSN origin, 3.4 mm at the first rib, and 4.1 mm at the distal clavicle. We present US data from asymptomatic subjects on the SSN and OM. Our results show that the SSN nerve CSA is consistent throughout the nerves proximal course. Furthermore, the OM and SSN tend to approximate as they course distally. Future studies with larger samples will better characterize the normal sonoanatomy of these structures between genders and across different ages. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: Suprascapular nerve Omohyoid muscle Ultrasonography
1. Background The suprascapular nerve (SSN) courses deep and parallel to the omohyoid muscle (OM) from its origin off the upper trunk of the brachial plexus in the lateral cervical region to its passage through the suprascapular foramen (Standring, 2008). The OM muscle begins as a superior belly originating from the hyoid bone, narrowing to a central tendon behind the sternocleidomastoid muscle, and continues as an inferior belly to attach to the medial aspect of the suprascapular foramen (Standring, 2008). The inferior belly of the OM is also known to variably attach to the superior transverse scapular ligament (Standring, 2008). During the act of deglutition, the OM functions to depress an elevated hyoid bone (Standring, 2008). Despite this intimate relationship, no research has described the potential for, or actual entrapment of, the SSN by the OM. Furthermore, there is no research describing the effects of seatbelt trauma on either the OM or SSN in whiplash injury, even though a considerable number of patients diagnosed with whiplash associated disorder present with combined neck and shoulder pain and altered scapular alignment (Hincapie et al., 2010; Helgadottir * Corresponding author. Tel.: þ1 (636) 230 1832; fax: þ1 (636) 207 2429. E-mail addresses: [email protected], [email protected] (P. J. Battaglia). 1356-689X/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.math.2013.12.005
et al., 2011). The aim of this current study was to quantify the in vivo anatomy of these structures in healthy subjects, so that future work may be done on symptomatic cohorts. The SSN is a mixed motor and sensory nerve receiving contributions from the C5 and C6 nerve roots, and occasionally the C4 nerve root (Freehill et al., 2012). The nerve supplies approximately 70% of the sensory innervation to the shoulder joint and provides motor innervation to both the spinatus muscles (Freehill et al., 2012). The SSN also has a variable cutaneous distribution (Ajmani, 1994). Suprascapular neuropathy has been shown to be absent in patients with cervical radiculopathy who present with shoulder pain (Date and Gray, 1996). However, cysts within the glenoid cavity can mimic cervical radiculopathy (Uppal et al., 1995), and ruling out cervical spine pain referral is important in the physical exam of shoulder pain (Date and Gray, 1996). Currently, no research has reported the cross-sectional area of the SSN in the lateral cervical region of the neck in patients with suprascapular neuropathy or cervical radiculopathy. Recent work on the use of ultrasonography (US) to assess the SSN at a level more proximal than the scapula was done by Siegenthaler and colleagues (Siegenthaler et al., 2012). In their study they performed US on 60 healthy volunteers and determined that visualization of the SSN with US is better in the lateral cervical region than at the level of the scapula and that the OM provided a
166
P.J. Battaglia et al. / Manual Therapy 19 (2014) 165e168
reliable anatomical landmark as it is clearly seen deep to the sternocleidomastoid muscle (Siegenthaler et al., 2012). Unfortunately, because their study was done to validate a novel nerve block approach, the only data provided was the nerve’s depth under the skin and distance to the brachial plexus (for nerve block safety). Also, the authors set a 1 min time limit per subject for their US scan to simulate the time constraints of their practice. This led to nonvisualization of the nerve in certain cases. Therefore, the purpose of this study was to obtain normative US data on both the SSN and OM in healthy subjects beginning at the SSN origin to as far distal as our scanning technique and participant anatomy would allow. Quantification of these structures with US may aid in future determination of suprascapular neuropathy or suspected OM damage and SSN entrapment/irritation.
standardized points: Point 1 (pt. 1), emergence of the nerve off of the superior trunk; Point 2 (pt. 2) lateral aspect of the first rib; Point 3 (pt. 3) most distal aspect of the clavicle which could be imaged. The OM was assessed in the long axis and diameter measurements were obtained at these same three standardized points. Vascular variants detected during the examination were also noted.
2. Method
A total of 33 healthy volunteers (11 female; age range 21e42; mean age 26.2 years) participated in the study. Descriptive results are presented in the Table 1. Of the 33 subjects, the dominant hand was scanned in five cases as these subjects reported mild neck and/ or shoulder discomfort on the non-dominant side. None of the subjects reported sustaining trauma to the neck or shoulder within the past three months. There were five right-sided and 28 left-sided scans. The SSN was easily visualized in all 33 scans (Figs. 1e4), and its cross-sectional area remained consistent through its visualized course in 29 of these scans. In the four nerves that changed size during their course, two increased from a value of 1 mm2 at their origin to 2 mm2, one decreased from a size of 3 mm2 at its origin to 2 mm2, and one measured 3 mm2 at its origin, 2 mm2 at the lateral aspect of the first rib, and 3 mm2 at the distal clavicle. When assessing for the distance from the OM to the SSN at the nerve’s origin, most subjects displayed consistent anatomy with the inferior belly being the portion of the muscle present. In three of our subjects the central tendon, not the inferior belly, was present adjacent to the origin of the SSN, with distances between these two structures of 7.5 mm, 8.6 mm and 11.8 mm respectively. One subject had the superior belly of the OM present at the SSN origin with a distance between the two of 6.4 mm and a long axis diameter of 2.6 mm. Four of our research participants had a blood vessel coursing between the SSN and OM.
2.1. Participants Participants were recruited internally through university advertisements and were selected if they were between the ages of 18e65 years, had no history of fracture, dislocation or surgery to the cervical spine or shoulder, reported no trauma to the cervical spine or shoulder within the past three months, and currently were not experiencing neck and/or shoulder pain. Presence of the following conditions also excluded participation from the study: diabetes mellitus, rheumatoid arthritis, neurofibromatosis, and myelopathy, radiculopathy and peripheral nerve entrapment. Patients were screened for the exclusion criteria by a senior intern with one year of experience in diagnosing and treating musculoskeletal conditions. Approval was obtained from the university institutional review board and each participant gave signed consent prior to participation. 2.2. Procedure US scans of all subjects were performed using a GE LOGIQ e US system with an 8e12 MHz linear transducer (GE Healthcare, Milwaukee, WI) operating at 10 MHz. All US scans were performed by the same board-certified chiropractic radiologist with six years of experience in musculoskeletal ultrasound. For the purpose of this study, no formal reliability testing was performed. Participants were gowned and seated in the same position for the duration of the scan, which was approximately 15 min. Each participant had their non-dominant lateral cervical region and supraclavicular fossa scanned. In instances when the participant reported either past trauma to the non-dominant side or a history of neck and/or shoulder pain in the last three months to the non-dominant side, the dominant side was used for scanning. When studying nerve cross-sectional area, it is acceptable to use the healthy contralateral side as an internal control (Tagliafico and Martinoli, 2013). The superior belly of the OM was identified immediately deep to the sternocleidomastoid muscle as it coursed from medial to lateral from its superior attachment to the hyoid bone. Identification was made with the transducer in the axial plane using a series of shortaxis linear slides in a superior to inferior direction. The superior belly of the OM was followed to its central tendon and inferior belly of OM and then as far inferiorly and laterally as possible until shadowing from the clavicle prevented further visualization. The C5 and C6 nerve roots were identified in the axial plane using previously established approaches (Siegenthaler et al., 2012) and were followed until they became the superior trunk of the brachial plexus. The SSN was identified as it emerged from the upper trunk of the brachial plexus at Erb’s point. Cross-sectional areas of the SSN as well as distances to the OM were measured at three
2.3. Data analysis Descriptive statistics were applied using Microsoft ExcelÔ 2010 (Microsoft, Inc., Bothell, WA). Mean, standard deviation (SD), SD range 2 and range were calculated. 3. Results
4. Discussion The SSN and OM follow similar courses through the lateral cervical region as they approach the scapula, and our results indicate that they are on average less than 1 cm apart during their Table 1 Descriptive statistics. Data point (n ¼ 33)
Mean
SD
SD range (2)
Cross sectional area (mm2) SSN e pt. 1 Cross sectional area (mm2) SSN e pt. 2 Cross sectional area (mm2) SSN e pt. 3 Linear distance (mm) OM to SSN e pt. 1 Linear distance (mm) OM to SSN e pt. 2 Linear distance (mm) OM to SSN e pt. 3 Long axis diameter (mm) of OM e pt. 1 Long axis diameter (mm) of OM e pt. 2 Long axis diameter (mm) of OM e pt. 3
1.9
0.4
(1.6)e2.4
2(1e3)
1.9
0.2
(1.8)e2.2
1(1e2)
2.0
0.3
(1.7)e2.3
2(1e3)
7.6
4.6
2.6e6.6
18.2(0e18.2)
4.2
4.0
2.0e6.0
12.4(0e12.4)
2.8
3.3
1.3e5.3
11.5(0e11.5)
2.4
1.0
(1.0)e3.0
4.1(0e4.1)
3.4
0.9
(1.1)e2.9
3.7(1.8e5.5)
4.1
0.9
(1.1)e2.9
3.6(2.4e6)
Range (minemax)
P.J. Battaglia et al. / Manual Therapy 19 (2014) 165e168
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Fig. 1. Short axis US image (left) and corresponding line diagram (right) of the SSN (arrowhead) and OM where the SSN emerges from the upper trunk of the brachial plexus (double arrowhead). The anterior scalene (AS) and middle scalene (MS) muscles are labeled to provide a reference for medial and lateral, respectively.
Fig. 2. Short axis US image (left) and corresponding line diagram (right) of the SSN and OM at the lateral aspect of the first rib. The trapezius muscle (asterisk) is also labeled.
Fig. 3. Short axis US image (left) and corresponding line diagram (right) of the SSN and OM at the distal clavicle. The trapezius muscle (asterisk) is also labeled.
Fig. 4. Long axis US image (left) and corresponding line diagram (right) demonstrating where diameter measurements were obtained on the OM (double vertical lines). The SSN is seen in long axis as a tubular structure (asterisk) immediately deep to the OM.
whole course from SSN origin until the distal clavicle, approximating during their path. Both the nerves cross-sectional area and the muscles diameter stay relatively constant within each individual subject, and narrow ranges exist for SSN cross-sectional area. Recent ultrasound work on the sciatic nerve in patients with sciatica and low back pain has demonstrated a significantly larger nerve on the affected side (Kara et al., 2012). Similar findings are
present in the median nerve in patients with carpal tunnel syndrome (French et al., 2012) and the greater occipital nerve in patients with unilateral occipital neuralgia (Cho et al., 2012). Although increases in nerve cross-sectional area appear to be attributable to local entrapment in both the median and greater occipital nerves, nerve root irritation from lumbar disc herniation may be an implicating factor in the increase in sciatic nerve cross-sectional
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areas in symptomatic persons (Kara et al., 2012). Presently, there have been no investigations into the relationship between SSN cross-sectional area in the lateral cervical region in subjects with suprascapular neuropathy or cervical radiculopathy. Our results provide preliminary normative data on the nerve cross-sectional area in this region. Clinically, the OM is implicated in what is known as the omohyoid sling syndrome, a condition that presents with a painless mass in the lower part of the neck apparent when swallowing but absent otherwise (Wong and Li, 2000). Patients may also present with difficulty swallowing or similar morbidities prompting surgical excision; however, operations are usually performed for cosmetic indications (Wong and Li, 2000). There is only one report in the orthopedic literature which describes the potential for brachial plexus irritation secondary to an increase in omohyoid size (Fiske, 1952). However, since Fiske’s report is of one subject, it is of little clinical utility. Furthermore, the findings presented in this report have not been reproduced since its publication over sixty years ago. Nevertheless, those who suffer from whiplash associated disorders rarely present with isolated neck pain and frequently the shoulder is also a significant source of discomfort (Hincapie et al., 2010). Additionally, scapular and cervical spine alignments change in those with both an insidious onset of neck pain and whiplash-associated disorder (Helgadottir et al., 2011). Since it attaches to both the scapula and hyoid bone, it is plausible that altered shoulder girdle and cervical spine alignment would also alter the contraction pattern or position of the OM. Moreover, considering the placement of the seatbelt constraint across the neck, the potential does exists for acute traumatic injury of the OM and brachial plexus in a whiplash injury. In our study, we could readily locate and follow both the OM and SSN from the nerve’s origin in the lateral cervical region to the distal clavicle. It would be feasible to assess for alterations in the size of the OM or identify an associated hematoma from acute trauma as well as assess the SSN cross-sectional area for nerve entrapment or irritation. Four of our subjects had a blood vessel coursing between the SSN and the inferior belly of the OM consistent with the superficial (transverse) cervical artery (Muhly and Orebaugh, 2011). In addition to variations in the vasculature of the lateral cervical region, variations of the OM could also pose challenges to accurate sonographic assessment. While we did not appreciate any variations in the OM, there are several reported variations of the omohyoid muscle (Rai et al., 2008). Also, the cleidoatlanticus muscle, which is variably present and courses from the clavicle vertically through the lateral cervical region to attach to the transverse process of the atlas, has also been reported to alter the ultrasound image of this area (Feigl and Pixner, 2011). This study has several limitations. Although an experienced examiner performed all of the scans and measurements, intra- and inter-examiner reliability was not established in this study. However, US has been shown to have good to excellent intra-patient, intra-examiner, and inter-examiner reliability in quantifying peripheral nerves of the upper extremity (Tagliafico and Martinoli, 2013). Furthermore, US is also valid, in addition to reliable, when measuring peripheral nerves and skeletal muscles (Cartwright et al., 2013). Considering the superficial nature of the SSN and OM, it is anticipated reliability in measuring these structures with US would be comparable. Also, although 33 participants may be an adequate sample size, this was a convenience sample and no power analysis was performed. There was also a marked gender discrepancy (11 female to 22 male) and differences in nerve size amongst sexes cannot be accurately assessed. Furthermore, as this was a young age cohort, it is unclear what the normative measurements would be in an older sample. Future studies with a larger sample, broader age range and matched symptomatic subjects and controls
will better characterize the sonoanatomy of these structures. The use of electronic calipers permits measuring cross-sectional areas to the nearest mm, so it is possible that sub-millimetric differences in nerve size were present that could not be observed, however their clinical significance is not known. Lastly, because patient clavicle size, morphology, and shoulder position is highly variable and produces an inconsistent amount of shadowing, using the distal clavicle as a reference point is arbitrary. Improvements in the scanning technique in which an assistant depresses the clavicle and scapula while imaging the more distal aspects of the SSN and OM may provide more optimal images. 5. Conclusion We have reported normative US data on the SSN and OM in young, healthy subjects. Future studies with larger samples will better characterize the normal sonoanatomy of these structures between genders and across different ages. Knowledge of these values may be of use in assessing cases of combined neck and shoulder pain, especially if there has been seatbelt trauma. Acknowledgment The authors would like to thank Frank Scali, DC, for his preparation of the line artwork. References Ajmani ML. The cutaneous branch of the human suprascapular nerve. J Anat 1994;185:439e42. Cartwright MS, Demar S, Griffin LP, Balakrishnan N, Harris JM, Walker FO. Validity and reliability of nerve and muscle ultrasound. Muscle Nerve 2013;47(4):515e21. Cho JC, Haun DW, Kettner NW. Sonographic evaluation of the greater occipital nerve in unilateral occipital neuralgia. J Ultrasound Med 2012;31(1):37e42. Date ES, Gray LA. Electrodiagnostic evidence for cervical radiculopathy and suprascapular neuropathy in shoulder pain. Electromyogr Clin Neurophysiol 1996;36:333e9. Feigl GC, Pixner T. The cleidoatlanticus muscle: a potential pitfall for the practice of ultrasound guided interscalene brachial plexus blocks. Surg Radiol Anat 2011;33:823e5. Fiske LG. Brachial plexus irritation due to hypertrophied omohyoid muscle. J Am Med Assoc 1952;149(8):758e9. Freehill M, Shi LL, Tompson JD, Warner JJP. Suprascapular neuropathy: diagnosis and management. Phys Sportsmed 2012;40(1):72e83. French C, Cartwright MS, Hobson-Webb LD, Boon AJ, Alter KE, Hunt CH, et al. Evidence-based guideline: neuromuscular ultrasound for the diagnosis of carpal tunnel syndrome. Muscle Nerve 2012;46(2):287e93. Helgadottir H, Kristjansson E, Mottram S, Karduna A, Jonsson H. Altered alignment of the shoulder girdle and cervical spine in patients with insidious onset neck pain and whiplash-associated disorder. J Appl Biomech 2011;27(3):181e91. Hincapie CA, Cassidy D, Cote P, Carroll LJ, Guzman J. Whiplash injury is more than neck pain: a population-based study of pain localization after traffic injury. J Occup Environ Med 2010;52(4):434e40. Kara M, Levent O, Tiftik T, Kaymak B, Ozel S, Akkus S, et al. Sonographic evaluation of sciatic nerves in patients with unilateral sciatica. Arch Phys Med Rehabil 2012;93(9):1598e602. Muhly WT, Orebaugh SL. Sonoanatomy of the vasculature of the supraclavicular and interscalene regions relevant for brachial plexus block. Acta Anaesthesiol Scan 2011;55:1247e53. Rai R, Ranade A, Nayak S, Vadgaonkar R, Mangala P, Krishnamurthy A. A study of anatomical variability of the omohyoid muscle and its clinical relevance. Clinics (Sao Paulo) 2008;64:521e4. Siegenthaler A, Moriggl B, Mlekusch S, Schliessbach J, Haug M, Curatolo M, et al. Ultrasound-guided suprascapular nerve block, description of a novel supraclavicular approach. Reg Anesth Pain Med 2012;37(3):325e8. Standring S. Gray’s anatomy: the anatomical basis of clinical practice. 40th ed. Spain: Churchill Livingstone Elsevier; 2008. pp. 442e820. Tagliafico A, Martinoli C. Reliability of side-to-side sonographic cross-sectional area measurements of upper extremity nerves in healthy volunteers. J Ultrasound Med 2013;32(3):457e62. Uppal G, Uppal J, Dwyer A. Glenoid cysts mimicking cervical radiculopathy. Spine 1995;20:2257e60. Wong DSY, Li JHC. The omohyoid sling syndrome. Am J Otolaryngol 2000;21(5): 318e22.
